The present invention pertains to a process for the polymerization of ethylene yielding a polymer with a broad distribution of molecular weights and having a considerable proportion of low molecular weights. The invention is particularly applicable to the production of linear high-density and low-density polyethylene. The result is obtained by means of the special treatment of the catalytic component, prior to its use with a cocatalyst in the polymerization of ethylene, and the specificity of the support of the said component.
The invention also pertains to the process for treating the catalytic component.
Polymerization of ethylene is understood to mean not only the homopolymerization of ethylene, but also the copolymerization of ethylene with an alpha-olefin such as propylene, butene-1 or 1-hexene, with the proportion of ethylene not being less than 66% by weight.
According to FR-A2,639,351, prior to use of the catalytic component, constituted of at least one derivative of magnesium, selected from among the compounds of formula Mg(OR.sub.2).sub.n Cl.sub.2-n, in which R.sub.2 is hydrogen or a linear or cyclical hydrocarbon radical and "n" is a number less than or equal to 2, and at least one chlorinated derivative of titanium in its form III and/or IV, it is subjected to reduction by a metal compound with at least one metal-carbon or metal-hydrogen bond, followed by treatment by a halogenated transition metal compound. This treatment of the catalytic component, which is subsequently employed in the catalytic system for the polymerization of ethylene, makes it possible to manufacture polymers with a broad distribution of molecular weights. Nevertheless, the resultant polymer contains less than 10% by weight of molecular weights lower than 10,000.